Pressure fluid follow-up servomotor system



Oct. 20, 1959 R. I Enuc i PRESSURE FLUID 'FoLLow-UP sERvouoroRsYsTEM Filed may 19, 1955 v 3' Sheets-Sheet. 'L

- Oct. 20, 1959 R. I Epuc v 2,909,156

FLUIDFOLLW-UP SERVOMOTOR SYSTEM l Filed nay 19, 1955 f s sheets-sheet 2 R. LEDUC PRESSURE FLUID FOLLOW-UP 'SERVOMOTOR SYSTEM oct. zo, 1959 3 sheets-sheet s md uw 19.1955

United. States Patent() PRESSURE FLUID 'FOLLOW-UP SERVOMOTOR SYSTEM Ren Leduc, Argenteuil, France Application May E19,1955, Serial No. 509,662

Claims priority, application France May 21, 1954 1 claim. (c1. 121-41) The present invention relates to a hydraulic control apparatus of a type suitable for use in modern aircraft, although itis to be understood that the present invention is not limited to use with aircraft.

In anaircraft which is manually controlled by the pilot it sometimes happens that forces outside of the -aircraft act on its control elements to shiftthese elements independently of their movement by the pilot.

It is an object ofthe present invention to `provide a hydraulic control apparatus which will automatically correct undesired movements of elements, such as aerofoil elements, of an aircraft without interfering withl the manual control of these elements.`

Also, it is an object of the present invention to provide a hydraulic control apparatus capable of converting an extremely small force into. a substantial movement of an element of the control apparatus.

A further object of the present invention is to combine a hydraulic control apparatus of the above type with a hydraulic jack.

Another `object of the invention is to provide substantial movement of a hydraulic jack wi-th an extremely small movement of fluid of, a hydraulic control apparatus connected to the hydraulic jack.

The objects of the present invention also include the provision ofl a structure capable ofaccomplishing all of the-above objects and, at the same time, made up of simple and ruggedly constructed parts Which are easy to assemble and disassemble and which are very reliable in operation. f

With the above objects inview, the present invention mainly consists of a hydraulic control apparatus which includes an elongated cylinder and an elongated rod means extending along the axis of the cylinder and carrying a piston which slidably engages the inner surface of the cylinder. A pair of conduits communicate with the cylinder, respectively, at opposite sides of the piston so that when one ofthe conduits communicates with a fluid yunder high pressure, and the other of the conduits communicates with a fluid under low pressure, the piston and rod means therewith will be shifted in one direction in the cylinder and so that the piston and rod means will be shifted in an opposite` direction when the other con-v "same respectively in communication with a Yfluid under lhigh-pressure and a fluid under low pressure when a small force-acts on-thedetecting `means so that thissmall force is converted into a substantial movement of'the piston and rod means. v

Thenovel featureswhich are considered-as characteristic'forthe -inventioncare set'forthin particular inthe 2,909,156 Patented Oct. 20, 1959 TCC appended claim. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will'be best understood from the following description of specific embodimentswhen read in connection with the accompanying drawings, inwhich Fig. 1 is a schematic illustration of a hydraulic -control apparatus constructed in accordance wit-h the present invention;

Fig. 2 schematically illustratesf'the'manner in which a different type of hydraulic control apparatus of the present invention is interconnectedwith a manual control structure of an aircraft and with an aerofoil element of an aircraft;

Fig. 3 shows a slightly differentv embodiment of the structure of Fig. 2; and v Fig. 4 is a schematic illustration of a different embodiment of the structure of Fig. l.

Referring to Fig. l, it will-be seen that the structure of the invention includes a source of iluid under relatively high -pressure in the form of -a pump ,1, which may be a gear. pump. -A bypfass bypasses kthe pump 1 and includes a valve 2, ydiagrammatically shown in Fig. l, this valve 2 together with the bypass maintaining the fluid discharged by the pump at a predetermined pressure in aknown way. Any other device for providing fluid at a predetermined pressure-may be used. The discharge conduit 13 of the pump 1 communica-tes 'with the 4cylinder 4 of the hydraulic detecting means-which detects lthe force F, diagrammatically indicated in Fig; l. A-rod 5 extends along the axis of the cylinder 4 and carries pistons 8-11, all of which slidably engage the inner surface of the cylinder 4. 'The pistons 8 and 11 are identical and the pistons9 and 10 are identical, pistons 8 and 9 forming one pair of pistons Iwhich arepseparated fromfthepair of pistons 10 and 11 by the intermediate chamber 12 in cylinderV 4which is included between the pistons 9 and 10. VThe pair of pistons 8 and 9 define Vbetween themselves an outer chamber 6 in the cylinder 4 and the pair of pistons 10 and 11 define between themselves an outer chamber 7 within thecylinder 4. The intermediate chamber 12 is in permanent communication with the conduit 13 supplied by the pump lwith a luid under high pressure. Chambers 6 and 7 are in permanent communication with conduits 14 and 15, respectively, these conduits leading toa cylinder 16 of a hydraulic means for converting the force F, even when the latter is extremely small, to a substantial movementof an element within the cylinder 16 as described below.

Chamber.6-communicatesthrough the opening 20 in the wall of cylinder 4 with a conduit 18 which forms an extension of a conduit 19 leading to a tank 17 provided with fluid to bepumped by thefpump 1, so that the conduit 18 serves asa source of. fluid under low pressure for the chamber 6. Chamber 7 communicates Awith the conduit.19. through the opening 21 in thewall of vcylinder 4. It will be noted from Fig. lV that the pistons 9 and 10 are very close to the openings 20. and 21, respectively,.and may even partially close these openings in the position of the parts shown in Fig. l so that upon movement of the 'rod 5 in either direction, one of-these openings will be v22 `and 23 will be closed while 4the other will be open.

The cylinder 16 accommodates an elongated rod-25 which extends-'along the y,axis of the cylinder-16 and which carries pistons 63, 26 and 50', all of which slidably engage the inner surface of the cylinder 16. The piston 26 separates chambers 27 and 28 in the cylinder 16 from each other, and it will be noted that the conduits 14 and 15, respectively, communicate with the chambers 27 and 28. The'pistons 63 and 50' are of equal diameter so that the fluid in the chambers 27 and 28 act on the same elective areas. The rod 25l further carriesa piston 24, one side of which engages a coil spring 29 and the other side of which'engages a coil spring 30.' Coil spring 29 abuts against a shoulder of the cylinder 16 and coil spring 30 abuts against the right en d wall of the cylinder 16, as viewedin Fig. l, so that the springs 29 and 30 cooperate with the piston 24 to yieldably maintain the piston 26 in the equilibrium .position indicated in Fig. 1'. All of the tree spaces within 'the cylinder 16 are lled with fluid and it will be noted that the iiuid on the left side of piston 63, as viewed in Fig. 1, communicates through conduit 33 with the tank 17, while the iiuid on the right side of piston 50' and surrounding the springs and piston 24 communicates through conduit 34 with the conduit 33.

The above described structure operates as follows:

If an. extremely small force AFacts in the direction of 4the arrow indicated in Fig. 1 on the extension 31 of rod 5, this rod 5 will be displaced to the right, as viewed in Fig. 1, through an extremely small distance, and the result will be that the opening 21 is closed to a greater degree by piston and the conduit 22 is closed to a greater degree by piston 9 while the opening 20 and the 'conduit 23 are opened to a greater degree. As a result, the conduit 14 communicates through conduit 18 with the 'tank 17 to have the fluid therein maintained at a low Vpressure P1, while the conduit receives iiuid under high pressure P2 from the conduit 13. This operation satisfies the relationship:

' in which k is the area of an annular section corresponding to the difference between the diameter of pistons 8 and 9. Of course, the difference between the diameter of the pistons 10 and 11V is the same. The value (P2-P1) is thus inversely proportional to k and as a result the hydraulic detector means formed by elements 4-11 is a device capable-of transforming an extremely small variation in force AF into a pressure differential which is substantial and which depends only upon the dimensional characteristics of the structure.

The pressures P1 and P2 are applied to the uid in 4` f ball members in engagement with the rotary cam. Each time the latter moves one of Ithe small pistons into the cylinder in which it slides .and away from the axis of rotation of the cam the pressure in one of the lines 14 or 15 is momentarily increased. Thus, in the position of the pulsator shown in Fig. l, the left small piston of the pulsator has just reached the end of its displacement to ward the line 14 to momentarily increase the pressure therein, and during the continued rotation of the cam the right small piston of the pulsator of Fig. l will be displaced toward the right to lincrease momentarily the pressure in the line 15. It is also possible to eliminate friction with any other suitable means, such as, for example, means impelling a rotary motion, around its axis, to the rod 5.

The rod 35 which forms an extension of the rod 25 may be used to control any desired structure. In the example shown in Fig. l,V and in accordance with the present inchambers 27 and 28, respectively, and thus these presbe compressed.

Thus, the structure of the invention is capable of transforming an extremely small variation of force AF-into a substantial displacement Ax with a sensitivity which depends only upon the dimensional characteristics of the structure.

In order to eliminate frictional forces a pulsator 32, or -its equivalent, is provided in the fluid circuit in accordance with the present invention, and preferably this pulsator 32 is located between the conduits 14 and 15, as indicated in Fig. 1. This Ipulsator maybe of any appropriate type and is diagrammatically illustrated in Fig. l. This pulsator includes the rotary 'cam shown in Fig. 1 which acts during its rotation onthe two small ball members shown in Fig. 1 to displace the latter horizontally so as to displace vention, this device which is controlled by the above described structure is a hydraulic jack or servo-control of any known type, such as those described in French Patents Nos. 1,003,822 and 1,034,741 in the name of Ren Leduc.

Thus,`it will be seen that in Fig. l the hydraulic jack includes an outer cylinder 36 in which a piston 61 reciprocates. The rod 35 has an extension 53 extending along the axis of the cylinder 36 and carries pistons 50 and 51 which are slidable within the cylindrical bore of the piston 61, as indicated in Fig. 1. The piston 61 denes with the inwardly extending annular flange S8 which slidably engages the piston 51, a chamber 56 which communicates through the conduit S4 with the pump 1 to receive iiuid under pressure therefrom.` A bore 49 in the piston 61 Y provides communication between chamber 56 and charnber 57 on the left side of piston 61 within the cylinder 36. The piston 61 is also formed with a passage 60 communicating with chamber 57 and with the inner bore of the piston 61, V the right end of the passage 60, as viewed in Fig. l, being closed in the position of the vparts shown in Fig. 1 by the piston 51. The piston 61 denes with the annular iiange S8 a chamber 62 which communicates through the conduit 55 with the tank 17, and it will be noted that the piston 61 is formed with an opening 52 communicating with the chamber 62 to maintain the fluid .in piston 61 to the right Vof piston 51, as viewed in Fig.

l, at a low pressure. The extension 48 of piston 61 is linked to any element ,to be controlled such as an aerofoil Velement on an aircraft.

jthe piston 61-to-the left in order to exactly balance the force of theV fluid in chamber 57 tending to move the piston 61 tol the right. In this way the hydraulic jack is ymaintained in'equilibrium. It the rod 25 is shifted to the right, then the rodl portion 53 also shifts to the right and the piston 61 simply follows this movement, the fluid in chamber 56 iiowing through passage 49 into chamber 57 .sov that the volume of chamber 57 increases vwhile the volume of chamber 56 decreases. On the other hand, if the rod 25 is moved to the left, Vthe right end ofpassagc 60, as viewed in Fig. 1, is opened to place the chamber 57 lat low pressure and the piston 61 then follows the rod of the invention may be mounted in an aircraft, and in Fig. 2 the cylinder 16 and structure carried therebyis combined with the cylinder 36 of the hydraulic jack and the small pistons engaging these ball members and acted l .upon by the springs shownin'Fig. 1 so as to maintain the -the 'structure-carriedthereby in a manner described below in connection with Fig. 4. Except for this change the and, whilethe conduits may be shown in Fig. 2 in a somewhat diierent arrangement, it will be appreciatedby a comparison of Fig. 2 with Fig. 1 thatthe same hydraulic interconnections are provided, the low pressure lines being indicated in Fig. 2 inthe shaded conduits. l

As may be seen from Fig. 2, the control stick 37, which is manually operated by the'pilot, acts on the aerofoil element 38 of the aircraft through any servo-mechanism 39 of a suitable construction, which is itself .actuated by the rod 40 linked to the ystick 37 through the medium of lever 41 andflink 43,' link 43 being pivotally connected to the bottom end o fstick 37 and to the bottom end of lever 41 at 42. The other end 44 of the lever41 is connected 'towhat corresponds to extension 48 of piston 61 of Fig. l, as-will beapparent from the description below, so-that as a result, with the arrangement .of Fig. 2, as long as no outside force Facts on the laircraft the top end 44 of lever 41- remains stationary and element 38 is manually controlled. In this 'case the lever 41 may be considered aspivoted at its top end on a stationary pivot. However, should-,an outside force of the above type act on the aircraft, then the structure ofthe invention will shift the top yend 44 ofv lever 41 to compensate for such a'force, and assuming that the vstick 37 remains stationaryat this time it will be seen that the lever-41! now pivots about its bottom end ito automatically -adjust the aerofoil 38. This force which acts on the aircraft may be derived froml any suitable device such as agyroscope and aneroid capsule, or any other suitable system capable of creating a force in response -to movement of the aircraft. The aerofoil velement to be controlled may be the elevators, the rudders Vor the aileron of the aircraft. l

- The-arrangement shown in Fig. 3 is identical with that of Fig. 2 except that the link '43 is connectedto therod T40 through a pair of interconnected bellcranks 45 yand 47. The point 44 Vat the end of the structure of the invention As-conneeted to anautomatic yieldable return device 46 -which is in turn connected to the bellcnank 45, as diagram- -maticallylindicated in Fig. 3. .This device46 servesto automatically return the control 37 to. acentralorrest `positon andmay have the structure shown in French Patent No. 1,049,257 in the name of Ren Leduc. Ex- -cept fori these differences, the structureofFig. 3 is identical withthat of Fig. 2. It will be seen, however,.fthat with the arrangement of Fig. 3 .the rest position of the control .stick 37 isdetermined. through the device 46 by the structure of the invention.

Fig. 4 shows the details ofhowthe cylinders 16 and `:36 lmay be combined together with the structure housed by vthese cylinders. VThe advantage of this compact arrangement of the structure is that only `an extremely. small Yamount ofuidiiowing along the conduits 14 and 15 is vrequired to provide a displacement ofthe hydraulic jack Awhich has the desired magnitude.

Referring to Fig. 4 i t will be seen that the cylinder16 forms anextension of the cylinder .36 and houses the -`piston 61 which itself forms a cylinder. along whose-axis :the rod extends. Thus, theschambers 27 and 28 re- ;spectivelylocated on opposite sides of the piston 26- carfried by rodz25 are now located directly within the hollow piston I61, the pistons 63 and 50 slidabl'y engaging the :inner surface of the piston 61. .The springs 29 and 30 are .engaged by parts integral with or iiXed to they cylinder .36 and .acton the rod 2 5 in thesamevway as the springs 29 and 30 of' Fig. 1,*these springs engaging a disc 24 in Fig. 4 in the same way as in Fig.-l. The hydraulic detector l:meansA--ll of Fig. v4,.ident'ical.witlr that of Fig. 1,.and

the conduits 14 and 15 communicate with annular chambers 68 and 69 formed in the inner surface of cylinder 16 in Fig. 4 and surrounding the piston 61, the latter being formed with openings 65 and 66 respectively communicating with chambers 68 `.and 69, `so that in this way the fluid in the lines 14 and 15 communicates through chambers 68 and 69, respectively, and through openings 65 and 66, respectively, with the chambers 27 and 28, respectively, so that the force F acting on the rod 5 through 6 the-extension 31 .thereof causesv displacement of.: rod 25 and piston 26-with respectto pistoni 61 inthe embodimento'fligfzdf.` y f I;

In the position'of .the partsV showninFig. 4 thegpiston 26 hasjust barelyfclosed the opening 66 which communicates withithe'fluid underpressure. Thusan"extremely small displacement of the fpiston.26 to the left,: as viewed in "Fig. i4,- places the "chamber128' in communication with thev liquid under pressure.

It-willbe noted that withtheiembodiment of Fig. 4, instead of two pistons 50. and 50as shown inFig. 1, va single piston 50 is'provided which cooperates with piston 26 to provide chamber 28. on the one hand, and .which Vcooperates with passage 49 in the same way as piston 50 of Fig. 1 to provide displacement of the piston161.

Thevremaining elements 'of Fig-4 Within .cylinder36 correspond to those vof Fig. 1 within thepcylinder36- and operate in the sameway. It willbe seen that with the structure of Fig. 4, ',when the pressure differential (P2-P1)provides a relatively'small displacement ofrod 25 with respect to piston 61, all of the structure associated withrod 25 and piston 61 is displaced, as is described in detail 'below,auntil the springs29 and 30 varetstressed suiciently vto .stop such movement. and,. as the. displacement of rod 25relative to piston 61xis iextremelyf small with the embodiment of Fig. 4, the amount ofliquid flowingthroughthe conduits 14 rand, 15 toprovide this displacement also is extremelysmall and, in fach-practically zero.` The advantage ofthis arrangement is an extremely great speedof action since the path of ow in the detector v4 -11 can be reduced to an extremely small-valuewhichis practically zero and, as a consequence, .an 'innitely small displacement of'therodS of the'hydraulic detector means (on the order of .only a fewilhundredths of a millimeter) is converted into awsubstantial displacement of the piston61.

AThe-'elements of Fig'. 4 which correspond tothose iof Fig. 2 1 areY indicated Vwith the :same :reference characters and it will be seen that the structure of;Fig. 4 includes the rod means 35-53, the differential piston .61 connected through extension 48 to the element to be controlled, the pistons 50-51 covering and uncovering the openings 49--52, the opening y49 being connected tothe iiuid under pressure through the conduit 54 which communicates Vwith chamber 57 which is inicommunication with passage 49 Vand the opening 52 communicating through chambers 62 with conduit; 55 leading to the tank17. Theopening 52 of Fig. 4 communicates in the same way as in Fig. `l

-with the passage to connect chamber 57 to the tank 17and the oriiice 52 and chamber 62'being separated from the chamber56 by the annular ange 58 which slidably engagessthe outer surface of the piston161 in the same way as in Fig. 1.

The following explanation of the operation ofjthe structure gives an understanding of how with a small displacement of rod 25 with respect to piston 61 an extremely small force F acting upon the hydraulic detector .and an extremely small flow of liquid are suflicient to .conduit 15 anda low vpressure in the conduit 14 which. at

this time communicates with the tank .17. As a result vthe chamber 28 of the hydraulic means 16 has the liquid therein placed at a higher pressure than the liquid in the chamber 27, and the rod 25 is thus displaced to the left, as viewed in Fig. 4. A very small displacement of the piston 26 to the left with the flow of a very small quantity of liquid may enter the chamber 28 results in a displacement of the piston 50 of Fig. 4 to the left, and as a result the passage 49 is opened so that the liquid under high pressure acts. upon the piston 61 to displace the latter Yof any desired variable factors. nate certain undesired movements of an aircraft, then tothe left, as viewed in Fig. 4, and as a result the piston 61 vshifts together with the rod 25, the elements 61 and 25 moving as a unit and without any relative displacement at this time. 'Under these conditions, the extremely small quantity. of liquid introduced into the chamber 28 has suiced to provide the required movement.v of the control element 48, while with the embodiment of Fig. 1, the piston 61 will continue to move only als long as the rod 25 moves in its housing. It is evident therefore that a greater quantity of liquid is required to produce the desired results with the embodiment of Fig. l'than with the embodiment of Fig. 4. In other words, with the embodiment of Fig. 4 the sensitivity of the response to the forces F and the rapidity'of this response are greatly improved.

The movement of the elements 25 and 61 to the left, as viewed in Pig.14, continues while the spring 29 becomes compressed until the resistance of the spring 29 to this movement exactly equals the pressure diierentiai (P2-P1) prevailing in the conduits 14 and 15. At this moment the rod 25 stops moving while the piston 61 still continues to moveuntil the passage 49 is closed by the piston 50 as a result of the relative movement. of the passage 49 with respect to the piston 50, and then the piston 61 stops moving.

The above described movements take place in the opposite direction when the direction of the force F is the `reverse of that shown in Fig. 4.

In addition, the openings 65 and 66 and chambers 68 and 69 enable conduits 14 and 15 to communicate with chambers 27 and 28, respectively, in the embodiment of Fig.- 4. The piston 61 is provided with an opening 64 communicating with the chamber to theV left of piston 63 and with annular chamber 67 formed in the outer cylinder portion 16, this chamber 67 communicating through conduit 33 with the tank 17. The chambers 67-69'are long enough to provide the desired displacement of the assembly 25-61 Withoutl interrupting the hydraulic connections.

As has been indicated above, the extension 31 of the hydraulic detectormeans may be subject to the inuence lf it is desired to'elimithe-element 31 can be placed under the influence of a gyroscope, shown schematically at 70 in Figs. 2 and 3. However, any other iniluences may be used, such as acceleration of the engine, its angular speed, its absolute speed, etc. v Y

The invention is not limited to the above described details since 'various modifications may be easily made by those 'skilled in the art. `In particular, the detector means 4-111'may be composed of only two pistons defining the intermediate chamber 12, the two outerl pistons 8 and 11 being eliminated and being formed simply by portions of the rod itself. l It will be understood that each of the elements described above, or two or'more together, may also nd a Auseful application in other types of hydraulic control apparatus differing fromthe types described above.

While the invention has been illustrated and described as embodied in combined manual and hydraulic control apparatus, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without department in any way from the spirit of the-present invention.

In a hydraulic control apparatus, in'combination, an outer cylinder having an inner surface portion formed with a passage extending axially along said outer cylinder, said outer cylinderhaving in its interior a chamber spaced from said passage; an inner cylinder slidable in said outer cylinder and having an annular outwardly'directed flange slidably engaging the interior of said outer cylinder insaid chamber thereof, said flange acting as a piston in said chamber of said outer cylinder, said inner cylinder being formed with a rst opening providing communication between said passage and the interior of said inner cylinder, and said inner cylinder being formed with additional openings providing communication between both ends of said flange and the interior of said inner cylinder; a first source of uid under pressure communicating with said passage of said outer cylinder; a second source 'of fluid 'under pressure communicating with said chamber of said outer cylinder; an elongated rod extending axially alongthe interior of said inner cylinder and carrying a pair of pistons one of which cooperates with said opening of said inner cylinder which communicates with said passage at the inner surface of said outer cylinder and the other of which cooperates with said additional openings of said inner cylinder for directing iluid under pressure from said second source from one to the other end of said flange to move said inner cylinder when the uid under pressure of `said rst source changes sufliciently to move said onepiston with respect to said opening of said inner cylinder which communicates with said passage, whereby an extremely smallamount of fluid of said first source. is su'icient -to position said other piston with respect .to said additional openings for causing the :duid under pressure of said second source to move said inner cylinder with respect to said outer cylinder through a vsubstantial axial distance; and spring means cooperating with said rod for yieldably resisting movementthereof, said inner cylinder, lrod, and pistons moving until the resistance produced by said spring means is suihcient to return said one piston to the position it had with respect to said opening of said inner cylinder which communicates with said passage before said one piston was influenced by the change in the pressure of said first source of fluid under pressure.

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